426 ' THE NERVOUS SYSTEM. 
this point there is absolutely no visible demarcation of the posterior column into 
two parts. : 
The white matter is not present in equal quantity throughout the entire length 
of the cord. It increases steadily from below upwards, and this increase 1s most 
an 
B.—Through the mid-dorsal region. 
1. Postero-median fissure. 
. is : 92. Postero-lateral groove. 
A.—Cervical region—at the level of the fifth cervical nerve. 3. Posterior cornu. 
(From a specimen prepared by Dr. A. Bruce.) 4. Posterior vesicular column of cells. 
: : z F 5. Lateral cornu. 
1. Postero-median fissure. 7. Formatio reticularis. 6. Central canal. 
2. Paramedian septum. 8. Central canal. 7. Anterior cornu. 
8. Postero-lateral groove. 9, Groups of ventral cells. 8. Antero-median fissure. 
4. Posterior nerve-root. 10. Anterior commissure. 
5. Substantia gelatinosa Rolandi. 11. Anterior nerve-root. 
6. Root-fibres entering gray matter. 12. Antero-median fissure. 
D.—Through the sacral region at the level of the 
third sacral nerve. (From a specimen pre- 
pared by Dr. A. Bruce.) 
C.—Through the lumbar region at the level of the 
fourth lumbar nerve. 1, Postero-median fissure. 
2. Posterior nerve-root. 
1. Posterior nerve-root. 5, Central canal. 3. Substantia gelatinosa Rolandi. 
2. Postero-median fissure. 6. Anterior commissure. 4. Posterior gray commissure. 
3. Substantia gelatinosa Rolandi. 7. Groups of ventral cells. 5. Anterior commissure. 
4. Root-fibres entering gray 8. Anterior nerve-root. 6. Antero-median fissure. 
matter. 9, Antero-median fissure. 
Fic. 320.—SEcTION THROUGH EACH OF THE Four REGIONS OF THE CorD. (From specimens prepared by 
the Weigert-Pal method.) 
noticeable in the lateral and posterior columns. In the lower part of the conus 
medullaris the amount of gray matter is actually greater than that of the white 
matter: but very soon this state of affairs is changed, and in the lumbar region the 
proportion of gray to white matter is approximately as 1:2°1; in the dorsal region 
